Signals: feeds made from your subscriptions, picked by Jev (#254)

A Signal is a name and keywords. A task beside DeadAir's asks TypeSafe's Jev, on the owner's own
key, about each item of their subscribed feeds from the last 30 days and every new one: one call
an item, one noul question for each of their Signals still to hear about it, 0.5 or more a fit.
Every verdict is kept, fitting or not, in signal_verdicts, so nothing is asked twice, and new
keywords drop a Signal's verdicts to be judged afresh. A key TypeSafe refuses (401/402/403) is
passed over until its owner saves another, so a bad key is not sent the whole queue.

A Signal's items come through entries_where with an EXISTS on its hits, so filters, search, sort
and read state are an ordinary list's, and reading an item in a Signal reads it in its feed.

The page shows Signals under the places, with New signal, and Settings takes the TypeSafe key,
which is never sent back. The browser suite stubs Jev in the fixture server (IPX_TYPESAFE_URL).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ipx/CHANGELOG.md

@@ -12,6 +12,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Signals: a feed you make from your own subscriptions, with keywords, holding the items TypeSafe's Jev says are about them, from the last 30 days and every new one, judged on your own TypeSafe key (`/api/signals`, and `typesafe_key` on `/api/me`) (#254).
+
 ### Changed
 
 - A feed that sends the same body again, as Patreon and Substack do whatever they are asked, is taken as unchanged instead of read again, and, without a schedule of its own, checked less often the longer it stays the same, up to every four hours, back on schedule when it changes (#242).